1. Technological Field
The present invention relates to an image reading apparatus and an image forming system including the image reading apparatus.
2. Description of the Related Art
A typical electrophotographic image forming apparatus forms a reference image for image quality control on a sheet, reads the reference image with a reader, and modifies the conditions for forming images in accordance with the read values acquired through reading of the reference image, to achieve uniform image quality.
The reader is provided with an image sensor (charged coupled device (CCD)), a lighting unit (light emitting diode (LED)) illuminating the sheet, and an optical system (including mirrors and a lens) for focusing the light incident on the sheet from the lighting unit on the image sensor.
Vibration of the image sensor or the mirrors of the reader causes a wavy read image or a shift in the reading position, leading to inaccurate reading of the image on the sheet.
Vibration sources of the reader include 1) collision of the leading edge of a sheet with conveying guides or other components; 2) impact of a sheet entering conveying rollers or impact of a sheet ejected from the conveying rollers; 3) a motor driving the conveying rollers; and 4) a fan motor for cooling disposed in the apparatus.
The magnitude of vibration caused by vibration sources 1) and 2) greatly varies depending on the physical properties of the sheet (for example, basis weight or stiffness), the size of the sheet, or the moving rate. A high moving rate and a wide range of available types of sheets are desirable in consideration of productivity.
A straight conveying path can reduce vibration caused by collision of a sheet with conveying guides even at a high moving rate and transfer of a very thick sheet. Moreover, a straight conveying path can reduce the contact force applied to the sheet travelling on the conveying rollers. This can reduce the load applied to the motor driving the conveying rollers and the vibration of the system.
However, a typical image forming apparatus cannot prevent vibration due to contact of the reader with the sheet because the reader partly defines the conveying path of the sheet (in detail, the faces of the conveying guides are disposed on the bottom face of the reader). Thus, the reader should avoid contact with other vibration sources as much as possible to achieve a satisfactory reading accuracy.
The reader includes a lighting unit including a light source, such as an LED or a halogen lamp. The lighting unit has a drawback of instable illuminance due to its heating. Thus, the light source should be cooled with a cooling fan.
A reader has been disclosed that includes a housing having two compartments partitioned with a wall and a cooling fan disposed in one of the compartments (for example, refer to Japanese Patent Application Laid-Open Publication No. 2009-267796).
As is disclosed in this patent publication, the cooling fan fixed to the housing of the reader including the lighting unit can cool the lighting unit at a closer distance.
However, such a cooling fan fixed to the housing of the reader transmits its vibration to the interior of the reader.
A possible configuration of the cooling fan is to be fixed to the housing of the reader via dampers. However, such a configuration causes an increase in the number of components and production costs.
Another possible configuration is fixing of the components of the reader, such as mirrors and a CCD, with dampers. Such a configuration not only causes an increase in the number of components and production costs but also unsatisfactory precision of the fixed positions of the components, such as the mirrors and the CCD.